Adrien-Marie Legendre quotes:

All the truths of mathematics are linked to each other, and all means of discovering them are equally admissible.

It is a matter for considerable regret that Fermat, who cultivated the theory of numbers with so much success, did not leave us with the proofs of the theorems he discovered. In truth, Messrs Euler and Lagrange, who have not disdained this kind of research, have proved most of these theorems, and have even substituted extensive theories for the isolated propositions of Fermat. But there are several proofs which have resisted their efforts.

These ... tables (values of trignometric functions), constructed by means of new techniques based principally on the calculus of differences, are one of the most beautiful monuments ever erected to science.